Target volume delineation of
rectal and anal carcinoma:
what are the differences?
By
Ola Mousa Elnady
Assistant Lecturer of clinical oncology
and nuclear medicine, MUH.
Anatomy of the rectum
• Length ranges from 12-15 cm (Figure 1).
• It is divided to upper, middle ,and lower thirds.
• Rectum begins at recto-sigmiod junction opposite
S3 vertebrae (buttom of sacroiliac joint), ends at
anorectal ring 1 inch below coccyx (at the level of
ischial tuberosity) (Figure 2).
• It forms 3 curvatures: lateral (RT, LT), perineal, and
sacral curvatures (Figure 3).
• Mesorectum: is adipose tissue around the rectum
carrying lymphovascular ,and neurological supply,
and encapsulated by fascia.
• The peritoneum covers the upper third only then
reflects to form the recto-vesical pouch in male,
recto-uterine pouch in female.
• Historically, tumors below the peritoneal reflection
have been treated as rectal cancers, while tumors
above treated as colon cancers.
• Recently, location of rectal t. is defined by distance
from lower edge of t. to anal verge, which is
determined accurately by rigid endoscopy.
• European and North American trials, have used a
cutoff of 16 or 12 cm above the anal verge
(respectively) to define rectal tumors.
Figure 1 : length, divisions of rectum.
Figure 2 : rectal anatomy (coronal view).
Figure 3 : rectal anatomy (sagittal view).
Spread of rectal cancer
Figure 4 : lymph node spread of rectal cancer.
Anatomy of the anal canal
• The anal canal extends from anorectal ring superiorly to
anal verge distally.
• With an average length of 4 cm (4.2 cm in male, 3.8 cm
in female). It is surrounded by the internal and external
anal sphincter muscle.
• The superior border is the anorectal ring, which is
located ~2 cm superior to the dentate line. The
transitional zone of the anus between the dentate line
and anorectal ring is where columnar epithelium of the
rectum meets the squamous epithelium of the anus. It
includes the columns of Morgagni.
• The distal end, i.e., anal verge is the junction of the
nonkeratinized squamous epithelium of the anal canal
and the keratinized hairy skin (Figure 5).
Figure 5 : anatomy of anal canal
(coronal view).
Spread of anal canal cancers
Figure 6 : lymph node spread of anal canal
cancers (intramural system of lymphatics ).
Rectal cancer Staging
PRIMARY TUMOR (T)
•
•
•
•
•
•
•
•
Tx: Primary tumor cannot be assessed
T0:No evidence of primary tumor
Tis: Carcinoma in situ: Intraepithelial or invasion of lamina
T1: Invasion of submucosa
T2: Invasion of musculosa
T3: Invasion into perirectal tissue
T4a: Invasion to the surface of visceral peritoneum
T4b: Invasion of or adherence to adjacent organs
or structures
LYMPH NODES (N)
• Nx: Regional LNs cannot be assessed
• N0: No regional LN metastasis
• N1a: Regional LN metastasis in 1 node
• N1b: Regional LN metastasis in 2-3 nodes
• N1c: tumor deposits in subserosa, mesentry,
non-peritonealized perirectal tissue + N0
• N2a: Regional LN metastasis in 4-6 nodes
• N2b: Regional LN metastasis in more than 7
DISTANT METASTASIS (M)
• Mx: Distant metastasis cannot be assessed
• M0: No distant metastasis
• M1a: Distant metastasis confined to one organ
(liver, lung, bone, non regional LN)
• M1b: Distant metastasis in more than organ or
the peritoneum
Anal cancer staging
PRIMARY TUMOR (T)
• Tx: Primary tumor cannot be assessed
• T0:No evidence of primary tumor
• Tis: Carcinoma in situ: Intraepithelial or invasion of
lamina
•
•
•
•
T1:tumor less than 2 cm in greatest dimension
T2: tumor 2-5 cm in greatest dimension
T3: tumor more than 5 cm in greatest dimension
T4: tumor of any size invades adjacent organs
LYMPH NODES (N)
• Nx: Regional LNs cannot be assessed
• N0: No regional LN metastasis
• N1: metastasis in perirectal LNs
• N2: Metastasis in unilateral internal iliac
and/or unilateral inguinal lymph node(s)
• N3: Metastasis in perirectal + inguinal lymph
nodes and/or bilateral internal iliac and/or
bilateral inguinal lymph nodes
DISTANT METASTASIS (M)
• Mx: Distant metastasis cannot be assessed
• M0: No distant metastasis
• M1: Distant metastasis (including seeding of
the peritoneum and positive peritoneal
cytology)
Stage grouping of anal carcinoma
Treatment guidelines for rectal cancer
Stage I (T1-2 N0 M0)
 Transanal rectal preserving excision if fulfilling criteria
 If proved to be higher stage  should do LAR or APR & receive adjuvant
CCRT & CTH
Stage II & III (T3-4 or N+)
 Preop. CCRT  surgery  Adjuvant CTH
 Surgery  Postop. CCRT  Adjuvant CTH
Stage IV
 If amenable to surgical resection : may benefit from
aggressive local therapy with preoperative chemoradiation therapy, followed
by surgical resection of both primary and metastatic lesions, adjuvant CTH .
 If not resectable : CTH +\- targeted therapy .
Locally recurrent disease : mainly in low pelvis & presacral
 Resectable  As new primary
 Unresectable CRT or CTH  surgery if become resectable
Treatment guidelines for anal cancer
Stage I (T1 N0 M0)
 Wide local excision if fulfilling criteria
 If R+ resection  should receive RTH, with or without CTH.
Stage II & III (T2-4 or N+)
 definitive CCRT is main ttt, equal to APR in terms of OS but
with sphincter preservation.
 Surgery after CCRT adds no benefits as proved by RTOG.
Locally recurrent or resistant T after CCRT :
Salvage APR ( with groin dissection in inguinal LN metastasis)
provides 5 ys OS 50%.
Radiation technique of rectal cancer
Patient position:
 prone on belly board for anterior displacement of bowel
or Supine.
 Comfortably full bladder may also reduce the dose to
small bowel, will be reproducible (by emptying the
bladder then drinking 200 ml of water 20 min before
planning).
Immobilization : by laser lines.
CT simulation:
• With I.V. contrast .
• With or without oral contrast 2 hours before CT scanning
which may be helpful to identify the small bowel.
•With a radiopaque anal mark at anal verge or below
rectal tumor in neoadjuvant RTH.
• Or with wire over perineal scar in adjuvant RTH after
APR.
CT cuts every 3 mm thickness from 1st lumbar
vertebrae till below anal verge.
Target Definition and Delineation:
• 3DCRT to deliver proper dose to the target volume
with the least dose to the risk structures
• IMRT not routinely used
• MRI or PET/CT can help in delineation by showing
the extent of the primary tumor and the regional LNs
metastasis
Target volume (neoadjuvant RTH):
The RTOG anorectal contouring atlas provides
contouring descriptions of three elective CTVs .
CTV-A: includes rectum, mesorectum carrying
primary tumor with the perirectal, presacral, and
internal iliac LNs and should be covered in all patients
with rectal cancer.
CTV-B: includes the external iliac nodes (covered only
in rectal cancer cases with T4 disease involving
anterior pelvic structure ).
CTV-C: includes the inguinal LNs (should be
considered in rectal cancer cases that extend into the
distal anal canal or lower third vagina).
CTV-A (upper pelvis):
• starts at L5-S1 to include
presacral space, internal iliac
LNs just after bifurcation of
common iliac Vs.
• Ant. extends 1-2 cm ant. to
sacrum to include presacral
space, 7 mm at least around
int. iliac Vs.
• Post. just in front of sacral
bone.
• Lat. till sacroiliac joints, stop at
medial borders of psoas major
ms.
CTV-A (mid pelvis):
• It includes rectum with
mesorectum, int. iliac LNs.
• Ant. CTV includes 1 cm from
ant. organ as internal margin
(bladder, SV, prostate, uterus).
• Posterolateraly ,it includes till
pelvic side wall ms, bone.
• It includes 7 mm at least
around internal iliac Vs to
encompass int. iliac LNs.
CTV-A (lower pelvis):
• Should
include
entire
mesorectum down to pelvic
floor ms (beginning of anal
canal if not involved) OR at
least 2 cm below gross
disease.
• Lateraly, only few mm beyond
levator ani ms is enough
unless there is invasion of
ischiorectal fossae, then we
should cover all invaded area
with 1-2 cm safety margin.
CTV-B (ext. iliac LNs)
• Delineated only in T4 tumors
involving anterior pelvic organ
(bladder, prostate, SV, uterus,
cervix).
• Cranially, it is delineated with int.
iliac LNs after bifurcation of
common iliac Vs then it starts to
migrate anteriorly , covered by 7
mm at least around ext iliac Vs.
• Caudally, it ends at level of
femoral heads.
CTV-C (inguinal LNs)
• Included only in T4 tumors
with distal anal canal or lower
vaginal extension.
• It starts cranially at femoral
heads or superior pubic ramus
just below level of end of ext.
iliac LNs.
• Caudally, till below ischial
tuberosity.
• Covered by margin 1-2 cm
around femoral Vs.
Target volume (adjuvant RTH):
• It is just the same as
neoadjuvant RTH , divided to
CTV-A, CTV-B, CTV-C but
observe:
• Cranially start at L5-S1 or 1 cm
cranial
to
anastomosis
whichever is most cephalid.
• Caudally, should include whole
mesorectal bed till pelvic floor
or 1 cm below anastomosis
whichever is most caudal.
• If post APR, should cover whole
perineum till perineal scar.
PTV
• Each CTV should be expanded by 0.5–1 cm,
depending on the physician’s comfort level with
setup accuracy, frequency of imaging.
OAR :
• The organs at risk include the small bowel, large
bowel (OR bowel bag), bladder, femoral heads.
• Uniform consensus guidelines for contouring the
small and large bowel, bladder, and femoral
heads are available from an RTOG consensus
panel.
• Suggested dose tolerence from QUANTEC and
RTOG 0822 :
Dose and Fractionation:
• For neoadjuvant RTH:
• Conventional fractionation to a total dose of 45
Gy to the entire pelvis, followed by a boost of
5.4 Gy to the tumor is recommended, using
high-energy (≥6 MV) photons. Patients with T4
disease or low-lying tumors may be boosted to
a total dose of 54 Gy.
• For adjuvant RTH:
• Conventional fractionation to a total dose of 45
Gy to the entire pelvis, followed by a boost of
5.4 Gy to the tumor bed is recommended, using
high-energy (≥6 MV) photons. Boost to a total
of 54 Gy if positive margin or persistant T4
tumors after neoadjuvant TTT.
Treatment Planning:
A Box technique or better three-field
arrangement (two laterals and a posterior–
anterior [PA]) allows some sparing of the
anterior pelvic structures such as small bowel,
bladder, and the external genitalia. Wedges or
other beam modifiers are used on the lateral
beams to improve dose homogeneity
Plan Assessment
• Ideally, at least 95 % of each PTV should
receive 100 % of the prescription dose. In
addition, the maximum dose in the PTV
should be <110 %.
• When evaluating plans with a sequential
boost to the gross disease, each individual
plan should be evaluated before the “plan
sum” to assess for areas that may be over- or
under-dosed.
Radiation technique of anal cancer
Patient position:
Supine with immobilization devices OR prone on
belly board (but ttt of inguinal LN by electron,
bolus can’t be done).
CT simulation:
The same as rectal ca (anal or perineal mark / IV
with or without oral contrast / comfortably full
bladder).
• Target volume:
The RTOG anorectal contouring atlas provides the
same three elective CTVs as rectal ca. but the
difference is that all 3 CTVs included in all cases of
anal ca. but with different doses depending on
stage (early or late).
CTV-A :includes rectum, mesorectum, perirectal
LNs, anal canal carrying primary tumor with the
perianal, presacral, and internal iliac LNs.
CTV-B: includes the external iliac nodes.
CTV-C: includes the inguinal LNs.
• Doses and Fractionation of different phases:
usually it’s given on 3 phases (differs from early&
advanced stage).
• Early stage (T1,2 N0):
• PHASE 1: 36 Gy/4ws (Low risk CTV)
include presacral, int. iliac LNs till buttom of sacroiliac joint, whole ext. iliac LNs, inguinal LNs.
PHASE 2: till 45 Gy/1.8/ fraction (high risk CTV)
include mesorectum, rectum, anal canal, int. iliac
LNs from below sacroiliac joint.
PHASE 3: boost on gross anal tumor (GTV-P) could
be given for T2 tumors till 50.4 Gy.
• advanced stage (T3,4 / N+):
PHASE 1: 36 Gy/4ws (low risk CTV)
include presacral, int. iliac, ext. iliac LNs till
buttom of sacro-iliac joint.
PHASE 2: till 45 Gy/1.8 / fraction (high risk CTV)
include mesorectum, rectum, anal canal with
perirectal LNs, uninvolved int., ext. iliac LNs from
below sacroiliac joint, uninvolved inguinal LNs.
PHASE 3: boost on gross anal tumor and any
involved LNs (GTV-P/ GTV-N) should be given till
50.4 - 54 Gy .
• CTV-P / CTV-N:
• CTV-P should cover the GTV-P with 1.5–2.5 cm
margin expansion but excluding uninvolved
bone, muscle, or air. The CTV-N should cover the
GTV-N with a 1.0–1.5 cm margin but excluding
uninvolved bone, muscle or air.
• PTV:
• Each CTV should be expanded by 0.5–1 cm,
depending on the physician’s comfort level with
setup accuracy, frequency of imaging.
• NB:
• RTOG 0529 (IMRT of locally advanced anal ca.,
2013) does not differentiate between highand low-risk regions so late stage anal ca.
treated by only 2 phases:
• The first phase till 45 Gy / 5 ws.
• The boost on gross disease till 50 or 54 Gy.
• OAR :
• The same as rectal ca but pelvic BM could be
added to minimize acute hematologic toxicity in
patients
receiving
concurrent
chemoradiotherapy for anal cancer. Delineation of the
pelvic bone marrow structure is described by
Mell et al. ( 2006). The pelvic bone marrow
consists of 3 subsites: the ilium, the lower pelvis,
and the lumbosacral spine which is the most
important site to be protected, mean dose
should be <28 Gy.
• Femoral heads:
should be outlined from
its top down to the
interface between the
greater
and
lesser
trochanters, including
notch of nutrient artery.
• Bowel bag:
including all small, large
intestinal loops within
the peritoneal space
starting from 5-6 cm
above PTV till its
caudal end.
• Treatment Planning:
• Plan Assessment: The same as rectal cancer.
• NB: slow regression of gross primary anal tumor
is common, complete response of anal ca. may
take 12 ms after end of CCRT to happen.
Pelvic irradiation complications:
 Toxicities and complications depend on the site,
volume irradiated ,and concomitant CTH.
 Acute effects include diarrhea, abdominal
discomfort/pain, increased frequency of urination,
dysuria, and skin irritation.
 Chronic or late toxicities include loose stools, rectal
urgency, infertility, ovarian dysfunction for
premenopausal women, vaginal stenosis, pelvic hair
loss, dry ejaculation for men, femoral head fracture,
and a small risk of late, secondary radiation-related
malignancy.
THANK
YOU